Fork Oil Question

Reading the manual of my 06' 450 last night in contemplation of changing fork seals/fluid. Looks like you fill the "inner fork cartridge" with fluid and then the outer tube with fluid. Anyone know how much mixing of this fluid there is? Is the inner component a sealed unit that maintains a constant amount of fluid, or does the amount in the inner cartridge vary as fluid moves in and out from the outer tube.



The design is for the fluids to remain separate. The inner cartridge is supposed to be purged of air, and has a piston and spring in it to separate air and oil. The outer chamber is then filled with a specific amount of oil for the purpose of lubing the forks, and for use in the hydraulic anti-bottoming forcing cones. Under most conditions, the fluids are kept separate from each other, and some, such as myself, use two different fluids. However, when the fork is bottomed, or nearly bottomed, the pressure against the cartridge seal is extremely high, and some oil can be forced past it from the outer to the inner chamber. The cartridge can deal with this, however, as it will self-bleed the excess back to the outer side once the level rises high enough, and the fork is fully compressed.

If using two differing fluids, and riding very hard, it's a good idea to change more often.

Thanks....exactly the info I needed. Is one body of fluid under more abuse and subject to more breakdown than the other?? Does one need more often changing than the other??


I'd say it's about even for differing reasons. The inner cartridge oil is subject to greater shear forces, since it does almost all the damping work, while the outer oil becomes contaminated with wear metals from the springs rubbing on the insides of the tubes. The condition of the inners is probably more critical.

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